This invention relates to antennas, and more particularly to compact antennas.
Past approaches for antenna design include spirals that are not sufficiently compact since their absorber cavities have generally been on the magnitude of a quarter wavelength (xcex) deep. For example, an antenna designed for a frequency of 10 gigahertz (GHz), which has a wavelength xcex of approximately one inch, requires a cavity of at least a quarter inch in depth. Since this past approach matches the cavity""s depth to that of the longest wavelength, it is not suitable for broadband operations.
Other past approaches for compact antennas include utilizing patch antennas. Patch antennas are relatively thin and can be on the order of 2% xcex in thickness. However, patch antennas are limited in bandwidth and are oftentimes too large for certain applications where space is considered a premium. Moreover, patch antennas cannot be dedicated to multioctave bandwidths.
Recently, a compact spiral antenna has been developed which overcomes some of the aforementioned disadvantages associated with conventional antennas. Commonly assigned U.S. Pat. No. 5,990,849 describes a compact spiral antenna with multioctave bandwidth capability. Nevertheless, this particular antenna also includes a cavity and thus is limited insofar as minimum thickness.
In view of the aforementioned shortcomings associated with conventional antennas, there exists a strong need in the art for an antenna which is both broadband and very thin. In particular, there is a strong need in the art for an antenna that can be employed without requiring adequate space for a cavity or the like. Moreover, there is a strong need for such an antenna which provides suitable gain (e.g, 8 dbi or more) for a variety of applications.
According to the present invention, a super thin, cavity free spiral antenna is provided. The antenna provides multioctave bandwidth capability with suitable gain, yet exhibits a very thin cavity-free profile.
The super thin, cavity free spiral antenna of the present invention is particularly suited for use in applications where space is at a premium. For example, the antenna of the present invention is useful in missiles where a smaller antenna allows more room for other electronics, etc. Also, the antenna of the present invention is useful in applications where aerodynamic drag or aesthetics is a concern. For example, the antenna may be mounted on the fuselage of an aircraft, the roof of an automobile, etc. Moreover, an antenna as thin as the present invention is suitable for mounting to a soldier""s helmet or onto the side of a military vehicle as a retrofit, for example. In such instances where no room exists to insert a thick cavity antenna within the bounds of the outer skin, the super thin, cavity free spiral antenna of the present invention may be retrofitted onto the outer skin itself.
In accordance with one aspect of the present invention, a super thin, cavity free spiral antenna is provided. The antenna includes a radiating element comprising a first spiral arm and a second spiral arm formed on a front surface of a first dielectric substrate. In addition, the antenna includes a resonant ground plane formed on a back surface of the first dielectric substrate. The resonant ground plane includes a second dielectric substrate having a front surface adjacent the back surface of the first dielectric substrate; a third spiral arm and a fourth spiral arm formed on the front surface of the second dielectric substrate, the third spiral arm and the fourth spiral arm being commonly aligned with the first spiral arm and the second spiral arm, respectively, on opposite sides of the first dielectric substrate; a fifth spiral arm formed on a back surface of the second dielectric substrate, the fifth spiral arm being generally commonly aligned with the third spiral arm and the fourth spiral arm, on opposite sides of the second dielectric substrate; and at least one impedance element coupling the third spiral arm and the fourth spiral arm to the fifth spiral arm to form a resonant circuit. The antenna further includes a feedline configuration coupled to the first and second spiral arms for transmitting/receiving a high frequency signal via the antenna.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.